Beyond the Bug: Reshaping the Immune Landscape - A New Era of Host-Directed Therapies for Tuberculosis

Tuberculosis (TB) remains a leading cause of infectious mortality worldwide. Although host inflammatory responses are essential for controlling Mycobacterium tuberculosis (Mtb), excessive or spatially dysregulated inflammation promotes granuloma necrosis, cavitation, tissue destruction, and transmission. Conventional antimicrobial therapy primarily targets the bacillus and does not directly resolve this host-pathogen paradox. Host-directed therapies (HDTs) are therefore evolving from broad immunomodulatory approaches, conceptualized here as HDT 1.0, toward mechanistically and spatially precise interventions, termed HDT 2.0.

This narrative review examines the granuloma as an integrated pharmacologic target and proposes a next-generation framework for HDT development that addresses the spatial, metabolic, immunologic, and structural features that permit Mtb persistence and limit sterilizing therapy.

Spatial transcriptomics, high-plex imaging, and advanced lesion profiling have revealed pronounced intralesional heterogeneity within TB granulomas, including avascular necrotic caseum, lipid-rich foamy macrophage zones, immune-excluded regions, and fibrotic cuffs. These microenvironments can restrict antibiotic penetration, impair T-cell trafficking and function, and create metabolically permissive niches for persistent bacilli. Accordingly, HDT 2.0 should address three interconnected therapeutic bottlenecks: improving drug access to poorly vascularized caseous lesions, disrupting lipid-dependent metabolic sanctuaries, and restoring spatially effective adaptive immunity without exacerbating immunopathology. Emerging approaches include spatially restricted immune-checkpoint modulation, itaconate-centered metabolic reprogramming, calibrated inflammasome targeting, investigation of IL-22-mediated epithelial protection, and controlled extracellular-matrix remodeling to improve antimicrobial delivery. Translation should follow a tiered strategy rather than assuming universal deployment of advanced technologies. Transcriptomic endotyping, spatial profiling, and PET-CT may be particularly valuable for patient enrichment, mechanistic phenotyping, and pharmacodynamic assessment in early-phase trials and specialized referral centers, whereas their limited accessibility in many high-burden and resource-constrained settings currently precludes their use as routine prerequisites for HDT implementation. Conventional microbiologic outcomes should also be complemented by mechanistically informative endpoints, including time-to-positivity, radiographic cavity closure, lesion resolution, and restoration of tissue-resident memory T-cell responses.

The next phase of TB therapeutics may depend not only on developing additional antimicrobials but also on dismantling the host-derived niches that sustain Mtb persistence. Treating the granuloma as a spatially organized, metabolically active, and immunologically heterogeneous therapeutic ecosystem provides a framework for developing precise HDTs that complement antibiotics, accelerate lesion sterilization, limit tissue damage, and potentially reduce relapse and transmission.